This invention relates to planar electronic substrates with radio frequency (RF) circuitry that are used to transmit and/or receive very high frequency RF signals in which signal isolation/separation is achieved using a magnetically based isolator or circulator.
Non-reciprocal devices such as circulators and isolators provide an important role in RF systems by providing high transfer efficiency for RF signals in one path while minimizing the transfer of RF signals in another path. For example, a 3-port circulator with the ports connected to the output of the transmitter, input of a receiver and an antenna permits the transmission from the transmitter of an RF signal to the antenna while simultaneously allowing a different frequency to be coupled from same antenna to the receiver to enable duplex operation. The simultaneous transmission and reception of different frequency RF signals is facilitated by the circulator which minimizes the coupling of the transmission RF signal to the receiver port while providing only a minimal loss between the transmitter and the antenna. Also, the received RF signal, which has a different frequency from the transmitted RF signal, is coupled from the antenna to the receiver with only a minimal loss.
Although circulators are used in duplex RF transmission systems, typical circulators have a large footprint relative to the wavelength of the subject high frequency RF signal. This limits the applicability of such circulators especially where physical space requirements and/or weight requirements are important. It will be appreciated that wavelength is inversely proportional to frequency so that for very high frequency RF signals the corresponding wavelength can be very small. There exists a need to minimize the size of a circulator/isolator to accommodate a minimum footprint on an RF substrate, especially at very high frequencies, so that the size of the substrate which includes a circulator/isolator is small relative to a wavelength.